Hepatitis E virus (HEV), the causative agent of hepatitis E, is an important public health problem in developing countries. HEV is also endemic in the U.S. The mortality rate is reportedly up to 20% in infected pregnant women. Due to the lack of a practical animal model and an in vitro cell culture system, the replication and pathogenesis of HEV is poorly understood and a vaccine for HEV is still not available. This proposal is based on our recent discoveries of a novel avian HEV from chickens in 2000 and a novel swine HEV from pigs in 1997. Both avian HEV and swine HEV are antigenically and genetically related to human HEV. We have shown that swine HEV infects non-human primates and a U.S. human strain of HEV infects pigs, and that pig handlers are at risk of zoonotic HEV infection. Avian HEV causes a hepatitis disease in chickens that is similar to human hepatitis E. The central hypotheses of this proposal are that hepatitis E is a zoonosis and that, like pigs, chickens are also animal reservoirs for HEV, and that chickens are a useful animal model system for HEV. The long-term objectives of the project are to define and understand the mechanism of HEV replication and pathogenesis by using HEV infection in chickens as an animal model system and by using avian-swine, avian-human and swine-human HEV chimeras to identify genes that are functionally important for these processes. In this proposal, we aim to: 1) systematically characterize the course of HEV replication and pathogenesis in a homologous model (avian HEV infection in chickens), 2) to identify the initial and extrahepatic sites of HEV replication in infected chickens, 3) to construct an infectious cDNA clone of avian HEV for future study of the structural and functional relationship of HEV genes by using HEV chimeras, and 4) to evaluate the potential risk of zoonotic infection by avian HEV. This will be accomplished by using standard techniques including in situ hybridization, PCR, cloning and sequencing, gene expression, and serological and pathological methods. The proposed studies will significantly advance our understanding of the mechanisms of HEV replication, pathogenesis and natural history. The information gained will be very useful for developing small animal models for HEV research and for devising strategies to prevent and control this important disease.